The present invention relates to a needle assembly for evacuated blood collection tubes or containers, one end of which needle is inserted into the vein of a blood examinee, and the other end of which is adapted to be communicated with the interior of a evacuated blood collecting container so as to be able to collect blood in an amount responsive to the negative pressure in said container.
A known needle assembly of this kind is illustrated in FIG. 1. In this device, a needle cannula support A is secured to the middle portion of a stainless needle cannula B, and one end of the needle cannula support A is provided with a rubber cap C for covering one end of the needle cannula B. With such kind of needle assembly, the other end, i.e. the tip of the needle cannula B, is inserted into the vein of a blood examinee and a blood collection container is fitted over rubber cap C and communicating onto the other end of the needle cannula so as to communicate with the interior of the blood collection container. Blood entering the collection container provides a first indication that the needle has accurately entered the vein of the blood examinee. If it is necessary to reinsert the needle in order to draw blood, the negative pressure pre-set in the blood collection container may be released resulting in an inability to collect a desired amount of blood or the need to employ a further blood collection tube.
To remove such demerits, a variety of needle assemblies have been proposed that are constructed in such a way that when inserted into the vein of the blood examinee a flow-out of blood can be confirmed. One known example is such that a needle cannula is divided into two sections, one of which is to be inserted into the vein and the other to be inserted into a evacuated blood collection container. A member connecting these two needle sections is provided with a transparent blood flow passage, and it is confirmed through this passage whether the blood is flowing or not. In another known example, the middle portion of a needle cannula is bored with a hole which is circumferentially formed with a blood flow confirmation chamber.
In the known needle assembly where the needle cannula is constituted by two needle sections, the member connecting the two needle sections requires a lot of components whereby manufacturing steps and cost increase. Moreover, unless the air not only inside the needle but also in the transparent blood flow passage within the member connecting the two needle sections flows out, the blood does not flow, so that the structure needed to solve these problems becomes complicated.
On the other hand, according to a needle assembly where the needle cannula is bored with a hole which is circumferentially formed with a blood flow confirmation chamber, the confirmation chamber must be retained under negative pressure or released to the outside, and therefore as in the above case, the structure becomes complicated and the manufacturing cost increases.
Furthermore, such kinds of blood collection needle assemblies are used for collecting multiple samples of blood from a blood examinee, ordinarily changing the blood collection container, and each time a sample of blood is collected, the rubber cap at one end of the needle cannula is punctured. Generally, the tip of a needle is obliquely cut and the tip point is sharpened (lancet-shaped). However, since the tip point is positioned at the outer periphery of a needle cannula, it is feared that in manufacturing needle assemblies for blood sampling the rubber cap might be impaired when it is mounted over the needle tip. Conventionally, therefore, the sharpened tip point is bent toward the center axis of the needle cannula or obliquely cut while retaining a round point shape. Needles having such bent tips substantially decrease the danger of impairing the rubber cap when the cap is mounted in manufacturing the needle assemblies. On the other hand, however, the rubber cap is apt to be hooked by a bent tip point when the cap is returned to its original position when a blood collection container is disengaged from the needle. Moreover, the bending step increases manufacturing cost. With a rounded point, the cutting opening of the rubber cap becomes wider when punctured with a needle. Accordingly, when repeatedly punctured by other evacuated blood collection tubes, the rubber cap tends to lose its sealing property whereby such a rubber cap is not suited for repeated sampling of blood.
Furthermore, these needle assemblies are disposable so that it is desired to provide them at as low a cost as possible. It is further required to guarantee safe and certain functioning so that the user such as doctor or nurse may not directly contact blood when blood is collected.